Transport Apparatus and Recording Apparatus

ABSTRACT

A transport apparatus includes a plurality of rollers that transport a medium, a detection unit that detects a rotation amount of each of the rollers, and a control unit that controls driving of each of the rollers. The control unit controls the driving of each of the rollers using a correction value that corresponds to a rotation amount from an origin position of the corresponding roller.

BACKGROUND

1. Technical Field

The present invention relates to transport apparatuses and recording apparatuses.

2. Related Art

There is a known recording apparatus in which a plurality of rollers for transporting a recording medium are provided, and the recording apparatus includes a transport control unit that controls the transport by applying a correction value to a roller, among the plurality of rollers, that is contributing to the transport, in each of transport regions of the recording medium (see JP-A-2012-101547, for example).

However, the stated apparatus has a problem in that the correction value that is applied is calculated based on a combination of a region of the recording medium, whose dimensions and the like are constant, and a roller, and thus it is difficult to calculate the correction value if the recording paper, the rollers, or the like are changed.

SUMMARY

Having been conceived in order to solve at least part of the aforementioned problems, an advantage of the invention is that a transport apparatus and a recording apparatus can be implemented as the following aspects or application examples.

Application Example 1

A transport apparatus according to this application example includes a plurality of rollers that transport a medium, a detection unit that detects a rotation amount of each of the rollers, and a control unit that controls driving of each of the rollers, the control unit controlling the driving of each of the rollers using a correction value that corresponds to a rotation amount from an origin position of the corresponding roller.

The medium is transported by the plurality of rollers. Here, there are cases where each roller used to transport the medium has an eccentricity amount unique to that roller. In such a case, the eccentricity in each roller produces variation in the feed amount of the medium. However, even if the rotation of a given roller is controlled based on a correction value for transport fluctuation in that roller, the medium is transported by a plurality of rollers, and thus the influence of transport fluctuation in the other rollers produces variation in the transport amount of the medium in the overall system that transports the medium. Accordingly, according to the aforementioned configuration, the respective rollers are synchronized by managing origin positions of the rollers, and correction is carried out using correction values that correspond to rotation amounts from the origin positions of the respective rollers used to transport the medium. Through this, it is easy to calculate correction for the plurality of rollers in the overall transport system, and thus the precision with which the medium is transported can be increased.

Application Example 2

In the transport apparatus according to the aforementioned application example, the plurality of rollers include an upstream-side roller and a downstream-side roller in a transport path of the medium.

According to this configuration, the correction is carried out using correction values corresponding to rotation amounts from the origin positions of the upstream-side roller and the downstream-side roller used to transport the medium, and thus the precision with which the medium is transported can be increased.

Application Example 3

In the transport apparatus according to the aforementioned application example, a circumference of the upstream-side roller is an integral multiple of a circumference of the downstream-side roller.

According to this configuration, it is easy to synchronize the upstream-side roller and the downstream-side roller, and correction control management is simplified as a result.

Application Example 4

In the transport apparatus according to the aforementioned application example, a distance between a position at which the upstream-side roller applies a transport force to the medium and a position at which the downstream-side roller applies a transport force to the medium is an integral multiple of the circumference of the upstream-side roller.

According to this configuration, the position at which the upstream-side roller applies the transport force to the medium matches the position at which the downstream-side roller applies the transport force to the medium when the medium is transported downstream. This makes the correction control even easier.

Application Example 5

A recording apparatus according to this application example includes a transport apparatus having a plurality of rollers that transport a medium, a detection unit that detects a rotation amount of each of the rollers, and a control unit that controls driving of each of the rollers using a correction value that corresponds to a rotation amount from an origin position of the corresponding roller, and a recording unit, the plurality of rollers being located upstream from the recording unit in a transport direction.

According to this configuration, in the transport apparatus, the respective rollers are synchronized by managing origin positions of the rollers, and correction is carried out using correction values that correspond to rotation amounts from the origin positions of the respective rollers used to transport the medium. Through this, it is easy to calculate correction for the plurality of rollers in the overall transport system, and thus the precision with which the medium is transported can be increased. Furthermore, the medium is transported relative to the recording unit by stable transport amounts, which makes it possible to form (record) high-resolution images.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanying drawings, wherein like numbers reference like elements.

FIG. 1 is a schematic diagram illustrating the configuration of a recording apparatus.

FIG. 2 is a schematic diagram illustrating the configuration of a transport apparatus.

FIG. 3 is a schematic diagram illustrating a configuration in the vicinity of a first roller.

FIG. 4 is a schematic diagram illustrating a configuration in the vicinity of a first roller.

FIG. 5 is a schematic diagram illustrating a configuration in the vicinity of a second roller.

FIG. 6 is a schematic diagram illustrating a configuration in the vicinity of a second roller.

FIG. 7 is a block diagram illustrating the configuration of a control unit of a transport apparatus.

FIGS. 8A and 8B are diagrams illustrating variation in transport amounts by a first roller.

FIG. 9 is a diagram illustrating correction data for a first roller.

FIGS. 10A and 10B are diagrams illustrating variation in transport amounts by a second roller.

FIG. 11 is a diagram illustrating correction data for a second roller.

FIG. 12 is a diagram illustrating correction data for first and second rollers.

FIGS. 13A and 13B are diagrams illustrating a method for controlling a transport apparatus.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, embodiments of the invention will be described with reference to the drawings. Note that the appended drawings depict the measurements of the various members and the like as different from their actual measurements in order to illustrate those members and the like at recognizable sizes.

First, the configuration of a recording apparatus will be described. The recording apparatus includes a transport apparatus having a plurality of rollers that transport a medium, a detection unit that detects a rotation amount of each of the rollers, and a control unit that controls driving of each of the rollers using a correction value that corresponds to a rotation amount from an origin position of the corresponding roller, as well as a recording unit; the plurality of rollers are located upstream from the recording unit in a transport direction. This will be described in detail hereinafter.

FIG. 1 is a schematic diagram illustrating the configuration of the recording apparatus. As illustrated in FIG. 1, a recording apparatus 20 is an ink jet printer, for example, and includes a transport apparatus 60 that transports roll paper P, which serves as a medium, in a sub scanning direction (a direction from the back to the front in FIG. 1). The recording apparatus 20 further includes a printer mechanism 41, which prints onto the roll paper P transported onto a platen 48 by the transport apparatus 60 by ejecting ink droplets from nozzles in a print head unit 44, which serves as a recording unit, while the print head unit 44 moves in a main scanning direction (a left-right direction, in FIG. 1). Note that a capping unit 48 b that seals a nozzle surface of the print head unit 44 is provided at one end of the platen 48 (a right end, in FIG. 1) in the main scanning direction, and a flushing area 48 a for carrying out flushing that ejects ink droplets from the nozzles of the print head unit 44 periodically in order to prevent the nozzles from clogging is provided at another end of the platen 48 (a left end, in FIG. 1) in the main scanning direction.

As illustrated in FIG. 1, the printer mechanism 41 includes: a carriage 42 capable of moving back and forth in the main scanning direction while being guided by a carriage guide 52; a carriage motor 54 and a slave roller 56 respectively provided at one end side and another end side of the carriage guide 52; a carriage belt 58 which is stretched between the carriage motor 54 and the slave roller 56 and is attached to the carriage 42; an ink cartridge 46, mounted in the carriage 42, that holds cyan (C), magenta (M), yellow (Y), and black (K) color inks, for example; the print head unit 44 in which are formed the plurality of nozzles that eject ink droplets upon the respective inks supplied from the ink cartridge 46 being pressurized; and so on.

The carriage 42 is moved back and forth in the main scanning direction by the carriage motor 54 driving the carriage belt 58. A carriage position sensor 49 that detects a position of the carriage 42 in the main scanning direction is attached to a rear surface side of the carriage 42. The carriage position sensor 49 is constituted by a linear-type optical scale 49 a disposed along the carriage guide 52 on a frame 59, and an optical sensor 49 b that is attached to the rear surface of the carriage 42 so as to face the optical scale 49 a and that optically reads the optical scale 49 a. A paper width detection sensor 43 for detecting a width of the roll paper P is attached to a bottom surface of the carriage 42. Although not illustrated in detail, the paper width detection sensor 43 is configured as a photodetector that includes a light-emitting element such as a light-emitting diode and a light-receiving element such as a phototransistor, and by emitting light from the light-emitting element and receiving light reflected by the roll paper P using the light-receiving element, converts a detected amount of light corresponding to a light intensity into an electrical signal as a voltage. The platen 48 and the roll paper P have different light reflectances, and thus by moving the carriage 42 across the roll paper P in the main scanning direction while the light-emitting element emits light, the paper width detection sensor 43 can detect left and right ends of the roll paper P based on the electrical signal obtained by the light-receiving element. The paper width can be obtained by finding a difference between two positions of the carriage 42 detected by the carriage position sensor 49 when the paper width detection sensor 43 has detected the left and right ends of the roll paper P.

Next, the configuration of the transport apparatus will be described. FIG. 2 is a schematic diagram illustrating the configuration of the transport apparatus. As illustrated in FIG. 2, the transport apparatus 60 includes a plurality of rollers that transport the roll paper P toward the print head unit 44 from a roll member 70 upon which the roll paper P is wound. In this embodiment, the plurality of rollers include a first roller 141 that serves as an upstream-side roller in a transport path of the roll paper P and a second roller 241 that serves as a downstream-side roller disposed downstream from the first roller 141 in the transport direction of the roll paper P. Note that the first roller 141 and the second roller 241 are positioned upstream from the print head unit 44 in the transport direction of the roll paper P. The first roller 141 is a driving roller, and is provided with a slave roller 142 that forms a pair with and is driven by the first roller 141. Likewise, the second roller 241 is a driving roller, and is provided with a slave roller 242 that forms a pair with and is driven by the second roller 241.

Meanwhile, as illustrated in FIG. 1, the recording apparatus 20 includes, as a control system thereof: a data/command analysis controller 22 that is inputted with various types of commands including print jobs from a control computer (control PC) 10, analyzes inputted commands, and executes necessary processing such as the generation of print data; a head controller 24 that is inputted with print data from the data/command analysis controller 22, and drives/controls the print head unit 44 to eject ink from the nozzles based on the inputted print data; and a printing mechanism/transport controller 30 serving as a control unit that controls the movement of the carriage 42, driving of the first roller 141 and the second roller 241, and the like. The data/command analysis controller 22, the head controller 24, and the printing mechanism/transport controller 30 communicate with each other via a communication port, and exchange control signals, data, and so on. Note that the data/command analysis controller 22, the head controller 24, and the printing mechanism/transport controller 30 each configure a microprocessor having a CPU as a central member thereof, the microprocessor including a ROM that stores processing programs, a RAM that temporarily stores data, an input/output port, and a communication port in addition to the CPU.

When, in the recording apparatus 20, image data is inputted to the data/command analysis controller 22 in accordance with a print instruction from the control PC 10, the data/command analysis controller 22 resizes the inputted image (RGB) data and carries out color conversion for converting that data into CMYK data, generates print data by binarizing the post-conversion CMYK data through carrying out halftone processing thereon, and sends the print data to the head controller 24 and the printing mechanism/transport controller 30. The printing mechanism/transport controller 30 then rotationally drives the first roller 141 and the second roller 241 using a driving unit so as to transport the roll paper P on the platen 48, and drives the carriage motor 54 so as to move the carriage 42 back and forth; the head controller 24 then causes the respective colors of ink to be ejected by driving the print head unit 44 at ejection timings based on the print data. A color image is formed on the roll paper P as a result.

Next, configurations in the vicinities of the first roller 141 and the second roller 241 will be described. FIGS. 3 and 4 are schematic diagrams illustrating a configuration in the vicinity of the first roller, and FIGS. 5 and 6 are schematic diagrams illustrating a configuration in the vicinity of the second roller. Note that FIGS. 3 and 5 are front views taken from the front relative to the transport direction of the roll paper P, whereas FIGS. 4 and 6 are side views taken from the side of the transport direction of the roll paper P.

First, the configuration in the vicinity of the first roller 141 will be described. Specifically, the configuration of a driving mechanism 151 that rotates the first roller 141 and the configuration of a first detection unit 171 serving as a detection unit that detects a rotation amount of the first roller 141 will be described.

First, the configuration of the driving mechanism 151 will be described. As illustrated in FIGS. 3 and 4, a slave pulley 161 is fixed to one end of a rotation shaft 141 a of the first roller 141, which is a driving roller. Meanwhile, a first drive motor 162, which is a DC motor, is disposed in a side area of the first roller 141, and a first driving pulley 163 is fixed to a drive shaft 162 a of the first drive motor 162. An endless timing belt 164 is stretched around the slave pulley 161 that is fixed to the rotation shaft 141 a of the first roller 141 and the first driving pulley 163 that is fixed to the drive shaft 162 a of the first drive motor 162, and as a result, the configuration is such that rotational force of the first drive motor 162 is transmitted to the first roller 141 via the timing belt 164 and the first roller 141 is rotated.

Next, the configuration of the first detection unit 171 will be described. As illustrated in FIGS. 3 and 4, a first rotary encoder 171 that serves as the first detection unit 171 is provided in the vicinity of the first roller 141. The first rotary encoder 171 is constituted by a slitted disk 172 that is fixed to the rotation shaft 141 a of the first roller 141 and a position detector 173 that is provided in a position through which an outer edge of the slitted disk 172 passes. A plurality of position detection slits 172 a are formed in the slitted disk 172 at equal intervals, along the entire outer edge thereof (only some are illustrated in FIG. 4). In addition, an origin position detection slit 172 b is formed in the slitted disk 172, further toward a center thereof than the position detection slits 172 a, at the same rotational position as that of an origin position provided in the first roller 141. The position detector 173 includes a light-emitting unit 173 a constituted by a light-emitting diode and a light-receiving unit 173 b constituted by a phototransistor that face each other with the outer edge of the slitted disk 172 located therebetween. The configuration is such that an electrical signal is outputted from the light-receiving unit 173 b upon the light-receiving unit 173 b receiving light from the light-emitting unit 173 a through the position detection slits 172 a or the origin position detection slit 172 b in the slitted disk 172.

Next, a configuration in the vicinity of the second roller 241 will be described. Specifically, the configuration of a driving mechanism 251 that rotates the second roller 241 and the configuration of a second detection unit 271 serving as a detection unit that detects a rotation amount of the second roller 241 will be described.

First, the configuration of the driving mechanism 251 will be described. As illustrated in FIGS. 5 and 6, a slave pulley 261 is fixed to one end of a rotation shaft 241 a of the second roller 241, which is a driving roller. Meanwhile, a second drive motor 262, which is a DC motor, is disposed in a side area of the second roller 241, and a driving pulley 263 is fixed to a drive shaft 262 a of the second drive motor 262. An endless timing belt 264 is stretched around the slave pulley 261 that is fixed to the rotation shaft 241 a of the second roller 241 and the driving pulley 263 that is fixed to the drive shaft 262 a of the second drive motor 262, and as a result, the configuration is such that rotational force of the second drive motor 262 is transmitted to the second roller 241 via the timing belt 264 and the second roller 241 is rotated.

Next, the configuration of the second detection unit 271 will be described. As illustrated in FIGS. 5 and 6, a second rotary encoder 271 that serves as the second detection unit 271 is provided in the vicinity of the second roller 241. The second rotary encoder 271 is constituted by a slitted disk 272 that is fixed to the rotation shaft 241 a of the second roller 241 and a position detector 273 that is provided in a position through which an outer edge of the slitted disk 272 passes. A plurality of position detection slits 272 a are formed in the slitted disk 272 at equal intervals, along the entire outer edge thereof (only some are illustrated in FIG. 6). In addition, an origin position detection slit 272 b is formed in the slitted disk 272, further toward a center thereof than the position detection slits 272 a, at the same rotational position as that of an origin position provided in the second roller 241. The position detector 273 includes a light-emitting unit 273 a constituted by a light-emitting diode and a light-receiving unit 273 b constituted by a phototransistor that face each other with the outer edge of the slitted disk 272 located therebetween. The configuration is such that an electrical signal is outputted from the light-receiving unit 273 b upon the light-receiving unit 273 b receiving light from the light-emitting unit 273 a through the position detection slits 272 a or the origin position detection slit 272 b in the slitted disk 272.

Next, the configuration of a control unit of the transport apparatus will be described. FIG. 7 is a block diagram illustrating the configuration of the control unit of the transport apparatus. A control unit 30 (the printing mechanism/transport controller 30) of the transport apparatus according to this embodiment includes a CPU serving as a computational processing unit, a storage unit such as a ROM that stores processing programs, a RAM that temporarily stores data, and the like, an input/output port and a communication port, and so on. As illustrated in FIG. 7, the first rotary encoder 171 and the second rotary encoder 271 are connected to the control unit 30. Likewise, the first drive motor 162 and the second drive motor 262 are connected to the control unit 30.

When the light-receiving unit 173 b of the first rotary encoder 171 outputs an electrical signal to the control unit 30 as a detection signal, the control unit 30 detects a rotational position of the first roller 141 that is fixed to the slitted disk 172 based on a square wave output signal from the encoder, which is obtained by carrying out waveform shaping on a detection signal formed of pulse signals produced by the light-receiving unit 173 b when light has passed through the portions of the position detection slits 172 a. In addition, the control unit 30 detects an origin position of the first roller 141 that is fixed to the slitted disk 172 based on a detection signal produced by the light-receiving unit 173 b when light has passed through the portion of the origin position detection slit 172 b. Meanwhile, when the light-receiving unit 273 b of the second rotary encoder 271 outputs an electrical signal to the control unit 30 as a detection signal, the control unit 30 detects a rotational position of the second roller 241 that is fixed to the slitted disk 272 based on a square wave output signal from the encoder, which is obtained by carrying out waveform shaping on a detection signal formed of pulse signals produced by the light-receiving unit 273 b when light has passed through the portions of the position detection slits 272 a. In addition, the control unit 30 detects an origin position of the second roller 241 that is fixed to the slitted disk 272 based on a detection signal produced by the light-receiving unit 273 b when light has passed through the portion of the origin position detection slit 272 b.

The configuration is such that when the detection signal is received from the first rotary encoder 171, the control unit 30 outputs, to the first drive motor 162, a driving control signal that has undergone a correction process based on first correction data stored in the storage unit of the control unit 30. The first correction data stored in the storage unit is tabled data containing differential amounts between theoretical and actual paper feed amounts of the first roller 141 produced by the first driving motor 162. Likewise, the configuration is such that when the detection signal is received from the second rotary encoder 271, the control unit 30 outputs, to the second drive motor 262, a driving control signal that has undergone a correction process based on second correction data stored in the storage unit of the control unit 30. Here, the second correction data is tabled data containing differential amounts between theoretical and actual paper feed amounts of the second roller 241 produced by the second drive motor 262. Note that the first and second correction data in the tables are not limited to the storage unit provided in the control unit 30, and the configuration may be such that the data can be communicated to the printing mechanism/transport controller 30 (the control unit 30) using an external storage unit such as a magnetic storage device, an optical disk, or the like.

Next, a method for controlling the recording apparatus and the transport apparatus will be described. However, variation in transport amounts of the roll paper P will be described before describing the method for controlling the recording apparatus and the transport apparatus. FIGS. 8A and 8B are diagrams illustrating variation in transport amounts of the first roller, where FIG. 8A is a diagram illustrating rotational positions of the first roller and FIG. 8B is a diagram illustrating feed amounts at rotational positions of the first roller. FIG. 9 is a diagram illustrating correction data for the first roller. Note that this embodiment describes a case where the circumference of the first roller 141 is an integral multiple of the circumference of the second roller 241 (specifically, double the circumference).

FIG. 8A illustrates a case where a rotational center O of the first roller 141 is shifted from a center position and is eccentric therefrom. Rotational positions when the first roller 141 rotates at equal angles with the rotational center O as an axis of rotation are indicated by A, B, C, D, E, F, G, and H on the outer ends of the first roller 141. As illustrated in FIG. 8B, in the case where the first roller 141 is eccentric, variation is produced in the feed amounts of the roll paper P during unit angle driving corresponding to the respective rotational positions A, B, C, D, E, F, G, and H. This results in similar variation being produced in the feed amounts of the roll paper P each time the first roller 141 rotates. Note that in the case where the rotational center O of the first roller 141 matches the center position, the feed amounts of the roll paper P during the unit angle driving corresponding to the respective rotational positions A, B, C, D, E, F, G, and H theoretically have constant values.

In the recording apparatus 20 (the transport apparatus 60) according to this embodiment, the feed amount of the roll paper P relative to the rotational position of the first roller 141 is measured; then, as illustrated in FIG. 9, data of position differential amounts between the actual feed amounts of the roll paper P in which variation occurs due to eccentricity (indicated by Y1 in FIG. 9) and the theoretical feed amount of the roll paper P occurring when the rotational center O of the first roller 141 matches the center position (indicated by X in FIG. 9) is found in advance, and the position differential amount data is stored in the storage unit as the first correction data.

Meanwhile, FIGS. 10A and 10B are diagrams illustrating variation in transport amounts of the second roller, where FIG. 10A is a diagram illustrating rotational positions of the second roller and FIG. 10B is a diagram illustrating feed amounts at rotational positions of the second roller. FIG. 11 is a diagram illustrating correction data for the second roller.

FIG. 10A illustrates a case where a rotational center O of the second roller 241 is shifted from a center position and is eccentric therefrom. Rotational positions when the second roller 241 rotates at equal angles with the rotational center O as an axis of rotation are indicated by A′, B′, C′, D′, E′, F′, G′, and H′ on the outer ends of the second roller 241. As illustrated in FIG. 10B, in the case where the second roller 241 is eccentric, variation is produced in the feed amounts of the roll paper P during unit angle driving corresponding to the respective rotational positions A′, B′, C′, D′, E′, F′, G′, and H′. This results in similar variation being produced in the feed amounts of the roll paper P each time the second roller 241 rotates. Note that in the case where the rotational center O of the second roller 241 matches the center position, the feed amounts of the roll paper P during the unit angle driving corresponding to the respective rotational positions A′, B′, C′, D′, E′, F′, G′, and H′ theoretically have constant values.

In the recording apparatus 20 (the transport apparatus 60) according to this embodiment, the feed amount of the roll paper P relative to the rotational position of the second roller 241 is measured; then, as illustrated in FIG. 11, data of position differential amounts between the actual feed amounts of the roll paper P in which variation occurs due to eccentricity (indicated by Y2 in FIG. 11) and the theoretical feed amount of the roll paper P occurring when the rotational center O of the second roller 241 matches the center position (indicated by X in FIG. 11) is found in advance, and the position differential amount data is stored in the storage unit as the second correction data.

FIG. 12 is a diagram illustrating correction data for the first roller and the second roller. That is, FIG. 12 illustrates a relationship between transport fluctuation in the first roller and transport fluctuation in the second roller. In this embodiment, because the circumference of the first roller 141 is double the circumference of the second roller 241, the rollers are in a relationship in which the second roller 241 makes two revolutions each time the first roller 141 makes a single revolution. By setting the circumference of the first roller 141 to an integral multiple of the circumference of the second roller 241 in this manner, it is easy to synchronize the first roller 141 and the second roller 241 as indicated in FIG. 12, which simplifies the correction control.

Meanwhile, FIG. 12 also illustrates a combined feed amount (indicated by Yc) obtained by combining the transport fluctuation of the first roller 141 and the transport fluctuation of the second roller 241. Based on this, it can be seen that transport variation arises in the feed amount of the roll paper P due to transport fluctuation of the first roller 141 and the second roller 241.

Next, the method for controlling the recording apparatus and the transport apparatus will be described. As mentioned above, eccentricity arises in the first roller 141 and the second roller 241, which necessitates a process for correcting transport fluctuation; however, for example, in the case where the transport fluctuation of the first roller 141 is great, even if the transport fluctuation is corrected for the second roller 241 alone, the correction for the second roller 241 alone will be insufficient and transport variation for the roll paper P will arise. Accordingly, in this embodiment, the control unit 30 controls the driving of the first roller 141 and the second roller 241 using correction values that correspond to rotation amounts from the respective origin positions of the first roller 141 and the second roller 241. This will be described in detail hereinafter.

FIGS. 13A and 13B are diagrams illustrating a method for controlling the transport apparatus. First, when the recording apparatus 20 is instructed to print, the control unit 30 of the transport apparatus 60 outputs the driving control signals to the first drive motor 162 and the second drive motor 262. Then, the first drive motor 162 and the second drive motor 262 are driven based on the driving control signals, and the first roller 141 and the second roller 241 rotate as a result.

Here, the control unit 30 detects the origin position of the first roller 141 based on the detection signal from the first rotary encoder 171, and outputs the driving control signal to the first drive motor 162 so as to rotate the first roller 141 from that detected origin position by an instructed rotation amount based on a transport instruction according to the print instruction and transport the roll paper P as a result. Likewise, the control unit 30 detects the origin position of the second roller 241 based on the detection signal from the second rotary encoder 271, and outputs the driving control signal to the second drive motor 262 so as to rotate the second roller 241 from that detected origin position by an instructed rotation amount based on a transport instruction according to the print instruction and transport the roll paper P as a result.

At this time, the control unit 30 retrieves the first correction data and the second correction data from the storage unit, calculates a difference between the differential amounts of the theoretical feed amounts and the actual feed amounts of the roll paper P by the first roller 141 and the second roller 241 based on the first correction data and the second correction data, finds a corrected rotation amount by correcting the instructed rotation amount so as to eliminate the difference between the differential amounts, and outputs the driving control signal so that the first roller 141 and the second roller 241 rotate by the corrected rotation amount.

Specifically, as illustrated in FIG. 13A, in the driving control for the first drive motor 162, a difference in differential amounts between the theoretical feed amount and the actual feed amount corresponding to the rotational position of the first roller 141 is found as a correction value; the correction value is subtracted from the instructed rotation amount in the case where the correction value is positive, and the correction value is added to the instructed rotation amount in the case where the correction value is negative. Likewise, as illustrated in FIG. 13B, in the driving control for the second drive motor 262, a difference in differential amounts between the theoretical feed amount and the actual feed amount corresponding to the rotational position of the second roller 241 is found as a correction value; the correction value is subtracted from the instructed rotation amount in the case where the correction value is positive, and the correction value is added to the instructed rotation amount in the case where the correction value is negative. In other words, the correction control is executed in a state in which the first roller 141 and the second roller 241 are synchronized.

For example, as illustrated in FIG. 13A, in the case where the first roller 141 is rotated from a rotational position C to a rotational position D, the differential amount between the theoretical feed amount and the actual feed amount (the hatched area in FIG. 13A) between the rotational position C and the rotational position D is positive, and thus that differential amount is taken as the correction value; the corrected rotation amount is then found by subtracting the correction value from the instructed rotation amount. On the other hand, in the case where the first roller 141 is rotated from a rotational position E to a rotational position F, the differential amount between the theoretical feed amount and the actual feed amount (the hatched area in FIG. 13A) between the rotational position E and the rotational position F is negative, and thus that differential amount is taken as the correction value; the corrected rotation amount is then found by adding the correction value to the instructed rotation amount. Through this, the first roller 141 is driven by the first drive motor 162 using the driving control signal that is based on the corrected rotation amount, and is thus rotated accurately using the origin position as a reference.

Likewise, as illustrated in FIG. 13B, in the case where the second roller 241 is rotated from a rotational position E′ to a rotational position G′, the differential amount between the theoretical feed amount and the actual feed amount (the hatched area in FIG. 13B) between the rotational position E′ and the rotational position G′ is negative, and thus that differential amount is taken as the correction value; the corrected rotation amount is then found by adding the correction value to the instructed rotation amount. On the other hand, in the case where the second roller 241 is rotated from a rotational position A′ to a rotational position C′, the differential amount between the theoretical feed amount and the actual feed amount (the hatched area in FIG. 13B) between the rotational position A′ and the rotational position C′ is positive, and thus that differential amount is taken as the correction value; the corrected rotation amount is then found by subtracting the correction value from the instructed rotation amount. Through this, the second roller 241 is driven by the second drive motor 262 using the driving control signal that is based on the corrected rotation amount, and is thus rotated accurately using the origin position as a reference.

The roll paper P is then transported toward the print head unit 44 by the first roller 141 and the second roller 241 rotating. Ink droplets are then ejected from the nozzles of the print head unit 44 onto the transported roll paper P. An image is formed on the roll paper P as a result.

According to the embodiment described thus far, the following effects can be obtained.

The instructed rotation amount based on a transport instruction is corrected using the first and second correction data, the corrected rotation amounts from the respective origin positions synchronized between the first roller 141 and the second roller 241 are found, the first roller 141 and the second roller 241 are rotated by carrying out driving control on the first drive motor 162 and the second drive motor 262. Through this, variations in the feed amount of the roll paper P when transporting the roll paper P using the first roller 141 and the second roller 241 can be reduced. Reducing variation in the feed amount of the roll paper P makes it possible to carry out high-resolution printing (image forming).

Note also that the invention is not limited to the embodiment described above, and many variations and alterations thereof are possible as well. Such variations will be described hereinafter.

Variation 1

Although the aforementioned embodiment describes the circumference of the first roller 141 as being an integral multiple of the circumference of the second roller 241, a distance between a position P1 at which the first roller 141 applies a transport force to the roll paper P and a position P2 at which the second roller 241 applies a transport force to the roll paper P may further be an integral multiple of the circumference of the first roller 141, as illustrated in FIG. 2. By doing so, the position P1 of the roll paper P at which the first roller 141 applies the transport force to the roll paper P matches the position P2 at which the second roller 241 applies the transport force when the roll paper P is transported downstream. This makes it even easier to carry out the correction control.

Variation 2

Although the aforementioned embodiment describes the circumference of the first roller 141 as being an integral multiple of the circumference of the second roller 241, the invention is not limited thereto. For example, the relationship between the circumferences need not be one in which the circumference of the first roller 141 is an integral multiple of the circumference of the second roller 241. Even with such a configuration, the transport fluctuation is corrected for the first roller 141 and the second roller 241 using the origin position as a reference, and thus the precision with which the roll paper P is transported can be increased.

Variation 3

Although the aforementioned embodiment describes correcting the driving signals for the first drive motor 162 and the second drive motor 262 in accordance with the correction of transport fluctuation in the first roller 141 and the second roller 241, the invention is not limited thereto. For example, as illustrated in FIG. 12, a correction process may be carried out on the driving control signal for the second drive motor 262 so as to offset a difference between the feed amount X and the combined feed amount Yc obtained by combining the transport fluctuation of the first roller 141 and the transport fluctuation of the second roller 241. Even with such a configuration, the correction is carried out in a state where the origin positions of the first roller 141 and the second roller 241 are managed, and thus the same effects as described above can be achieved.

Variation 4

Although the aforementioned embodiment describes an example in which the medium is the roll paper P, the invention is not limited thereto. For example, the medium may be single sheets of paper that are separated one sheet at a time. The same effects as those described above can be obtained even with such a configuration.

The entire disclosure of Japanese Patent Application No.2014-153661, filed Jul. 29, 2014 is expressly incorporated by reference herein. 

What is claimed is:
 1. A transport apparatus comprising: a plurality of rollers that transport a medium; a detection unit that detects a rotation amount of each of the rollers; and a control unit that controls driving of each of the rollers, wherein the control unit controls the driving of each of the rollers using a correction value that corresponds to a rotation amount from an origin position of the corresponding roller.
 2. The transport apparatus according to claim 1, wherein the plurality of rollers include an upstream-side roller and a downstream-side roller in a transport path of the medium.
 3. The transport apparatus according to claim 2, wherein a circumference of the upstream-side roller is an integral multiple of a circumference of the downstream-side roller.
 4. The transport apparatus according to claim 2, wherein a distance between a position at which the upstream-side roller applies a transport force to the medium and a position at which the downstream-side roller applies a transport force to the medium is an integral multiple of the circumference of the upstream-side roller.
 5. A recording apparatus comprising: a transport apparatus including a plurality of rollers that transport a medium, a detection unit that detects a rotation amount of each of the rollers, and a control unit that controls driving of each of the rollers using a correction value that corresponds to a rotation amount from an origin position of the corresponding roller; and a recording unit, wherein the plurality of rollers are located upstream from the recording unit in a transport direction. 